This invention relates to an internal combustion engine in which the air-to-fuel ratio of the air-fuel mixture supplied into the combustion chambers of the engine is controlled utilizing feedback techniques in accordance with the composition of the exhaust gases discharged from the combustion chambers of the engine.
As is well known, it is now required from the standpoint of exhaust gas control and fuel economy to accurately control the air-to-fuel ratio of the air-fuel mixture supplied into the combustion chambers of an internal combustion engine at a required value. Especially when the exhaust system of the internal combustion engine is equipped with a three-way catalytic converter capable of reducing nitrogen oxides as well as oxidizing hydrocarbons and carbon monoxide, the three-way catalytic converter requires to be supplied with exhaust gases produced by combustion of the air-fuel mixture having approximately stoichiometric air-to-fuel ratio in the combustion chambers in order to allow the converter to function effectively and sufficiently. However, usual carburetors cannot accurately control the air-to-fuel ratio of the mixture supplied therefrom due to their constructions and characteristics.
In order to satisfy the above requirements, it has been proposed that the air-to-fuel ratio of the mixture supplied into the combustion chambers is controlled at the stoichiometric air-to-fuel ratio utilizing feedback techniques wherein the fuel amount supplied into air inducted into the combustion chambers is directly or indirectly regulated in response to the composition of the exhaust gases which composition are detected by an exhaust gas sensor located in an exhaust passage communicated downstream of the combustion chambers of the engine. This method has been realized depending on the fact that the composition of the exhaust gases are in close relationship with the air-to-fuel ratio of the mixture supplied into the combustion chambers of the engine. In a system for performing the above method, solenoid actuated valves or electromagnetic valves which are operated in an energizing and de-energizing or on an off manner have been usually employed as actuating means for regulating the flow amount of the fuel supplied into the combustion chambers.
However, this system employing such a type of valves has encountered the difficulty wherein the air-to-fuel ratio of the mixture suplied into the combustion chambers is abruptly and instantaneously changed within a range since the pulsation of the fuel flow regulated by the above valves is generated when the solenoid valves are energized to open allowing the fuel to flow or de-energized to close forcing to stop the fuel flow. The pulsation of the fuel flow may cause the irregularity of fluctuation of the engine revolution in cooperation with intake air pulsation which is occured by the open and close action of intake valves of the engine. This inevitably invites deterioration of the driveability of the engine and failed exhaust gas control.